Process for preparing phosphorus-reduced cow milk

ABSTRACT

The phosphorus-reduced cow milk of the invention contains a reduced proportion of phosphorus of 1.0 g to 2.0 g per 100 g of protein in the cow milk, the weight ratio of phosphorus to calcium being 1:2, nearly the same as that of human milk. The ratio is most adequate for calcium absorption and is suitable as food for kidney-disease patients with reduced calcium-absorbing function, persons of old age and hyperphosphatemia patients. Moreover, the phosphorus-reduced cow milk of the invention in which only phosphorus component is selectively removed and none of other component is lost maintains the value of cow milk as perfect food.

TECHNICAL FIELD

The present invention relates to phosphorus-reduced cow milk and aprocess for preparing the same. More particularly, it is concerned withphosphorus-reduced cow milk only phosphorus content of which is reducedand a process for preparing phosphorus-reduced cow milk which comprisessubjecting milk the serum to reduction treatment of a phosphoruscontent.

The phosphorus-reduced cow milk according to the invention is valuableas food for hyperphosphatemia patients, kidney-disease patients withcalcium-absorbing function impaired and persons of old age.

BACKGROUND ART

Cow milk is an excellent food containing almost all nutrients and wellabsorbed by digestion and is especially suitable as a diet for the sick.Weight ratio of phosphorus to calcium in cow milk (0.9:1), however, isundesirable from the viewpoint of calcium absorption, becauseapproximately 42% of the calcium in the milk exists in colloid phasesuch as phosphate salts which is in difficultly absorbable state. It isdesirable from the viewpoint of calcium absorption that weight ratio ofphosphorus to calcium in food is around 1:2 as it is in human milk.Higher levels of phosphorus than the above will form calcium phosphateto insolubilize the calcium and hinder absorption of the calcium.Whereas phosphorus excess in such a degree as mentioned above does notcause troubles in healthy persons, it is desired to decrease phosphoruscontent in cow milk to a phosphorus to calcium ratio of about 1:2 whentaken by kidney-disease patients with deteriorated calcium-absorbingfunction, persons of old age, patients with calcium-metabolismabnormality, and hyperphosphatemia patients. For this purpose,phosphorus in cow milk which is contained in an amount of approximately3 g per 100 g of protein should be reduced to 1.0-2.0 g.

Heretofore, for reducing phosphorus content in cow milk there are knowna process according to which an alkali solution of casein separated fromcow milk is heattreated at 60°-150° C. for 2 sec. to 60 min. and thetreated casein solution is subjected to an ion-exchange treatment(Japanese Patent Publication No. 25697/1971) and a process according towhich skimmed milk is acidified to a pH of 5.2 -6.0 and the acidifiedskimmed milk is passed through an ion-exchange material (Japanese PatentLaid-open to Public No. 256342/1985).

According to the above-mentioned prior-art methods, the treatment withan ion-exchange material is associated with a disadvantage that otheruseful acid and mineral components are also removed together withphosphorus, although the phosphorus content in cow milk can be reduced.Process by means of a membrane dialysis instead of an ion-exchangematerial which is also known is disadvantageous in that nutrients with amolecular weight similar to that of phosphorus are simultaneouslyremoved.

Therefore, the object of the invention is to provide phosphorus-reducedcow milk with the content of only phosphorus in cow milk reduced to thedegree that is contained in human milk and a process for preparing thesame.

DISCLOSURE OF THE INVENTION

The first of the invention comprises phosphorus-reduced cow milk onlythe phosphorus content of which is reduced to a proportion of 1.0-2.0 gper 100 g of protein.

The second invention is concerned with a process for preparing theabove-mentioned cow milk which comprises adding an acid and/or rennet tocow milk to cause agglutination of casein, separating the agglutinatedcasein, adding to the remaining milk serum a calcium salt to precipitatefree phosphoric acid contained in the milk serum as calcium phosphatewith lower solubility, removing the calcium phosphate, adding to theremaining solution the above-separated casein to a phosphorus content of1.0-2.0 g per 100 g of protein and then emulsifying the product.

"Cow milk" as used herein as the starting material may be any of rawmilk, ordinary milk, processed milk and skimmed milk produced byremoving cream by centrifugal separation. Such liquid milk usuallycontains 0.09-0.10% of phosphorus while containing 2.9-3.6% of protein,proportion of the phosphorus to the protein being approximately 3%. Asthe cow milk may also be used a reconstitution product of commerciallyavailable skim milk powder redissolved in water. Phosphorus content ofthe product is almost the same as that of cow milk.

"Casein" is phosphoprotein which is the main component of milk proteinsand exerts property as being precipitated at the isoelectric point whenpH is adjusted to 4.6 by adding an acid to the milk.

"Milk serum" is a clear greenish yellow solution remaining after removalof the casein precipitates formed by adding an acid or rennet to cowmilk or skimmed milk. Protein and phosphorus contained in milk serum areabout 0.3-0.7% and 0.063-0.071%, respectively.

First, according to the process of the invention, an acid is added tothe starting cow milk or skimmed milk, or as needed, rennet is reactedto precipitate casein. There is no particular limitation to the natureof the acid, and such an acid as hydrochloric, lactic, acetic orsulfuric acid is preferably employed. Amount of the acid to be added isvariable and is such that pH of the resulting solution is in the rangeof 4-5 and preferably around 4.6. The temperature during the additionmay be room temperature. "Rennet" is a name of the enzyme product usedfor coagulation of cow milk, which is a protease. The addition of rennetmay be performed either in place of or in addition to the addition of anacid. If rennet is used, it is uniformly mixed with stirring in aproportion of 0.002-0.004% by weight against the starting cow milk. Inthis case, addition of 0.02% by weight of calcium chloride to the cowmilk and adjustment to a pH of around 4.8 and a temperature of 30°-40°C. facilitate coagulation of casein.

As described above, addition of an acid or action of rennet precipitatescasein, which is isolated by centrifugal separation (at approximately1000 rpm for about 5 min.) or by filtration. From the remainingsupernatant, or milk serum is removed phosphorus by the calciumprecipitation method.

The calcium precipitation method represents a method which involvesinsolubilizing free phosphoric acid contained in milk serum in the formof calcium phosphate with lower solubility to precipitate it.

To the milk serum thus obtained is added approximately 0.1% by weight to2.0% by weight of a calcium salt, preferably calcium chloride. It isnecessary to add 3 moles or more of the calcium salt per 2 moles ofphosphoric acid in the milk serum. The calcium phosphate thus formed isprecipitated by adjusting pH to 6.5-7.0 by the addition of sodiumhydroxide or the like. The white crystalline calcium phosphate isremoved by centrifugal separation (at approximately 1500 rpm for 5 min.)or by filtration. It is only calcium phosphate that is precipitated inthe above-mentioned pH range, in which calcium lactate and others arenot precipitated so that none of valuable nutrients in cow milk exceptphosphorus is lost.

The solution obtained by the dephosphorylation treatment is mixed withthe previously separated casein and the mixture is homogenized whileadjusting pH to 6.5-6.7 by the use of sodium hydroxide or the like.

If skimmed milk is employed as the starting material, milk fat (cream)is subsequently added, and additives such as an emulsifier are added asneeded. Subsequently, the mixture is heated to a temperature of 50°C.-60° C., thoroughly stirred and emulsified in a homogenizer underpressure of at 100 kg/cm² -500 kg/cm², preferably 200 kg/cm² and thenheated to a temperature of 60° C.-65° C. for stabilization. Phosphoruscontent of the emulsion thus obtained is about 20-50% as compared withthe starting cow milk and, an efficiency of phosphorus-reduction is ofabout 50-80%. If desired, the emulsion can be filled in a container suchas paper pack, aluminum pack or can, sterilized and utilized asphosphorusreduced cow milk. The emulsion may also be subjected to spraydrying treatment to prepare a powdered milk product.

The invention will be described below in more detail with reference toan example.

EXAMPLE 1

1200 ml of commercially available cow milk (nonstandardized) wassubjected to a centrifuge (at 3,000 rpm for 20 min.) for separation ofthe cream layer to prepare approximately 1,000 ml of skimmed milk.Weight of protein and phosphorus contained in the skimmed milk were 2.67g/100 ml and 93.1 mg/100 ml, respectively (corresponding to 3.49 g ofphosphorus per 100 g of protein). The skimmed milk was adjusted to a pHof 4.6 with 2N hydrochloric acid, and casein was thereby precipitated.

The whole mass was subjected to a centrifuge (at 3,000 rpm for 10 min.),and to the precipitates was added water to collect 100 ml of the caseinfraction.

Separately, 950 ml of the supernatant was collected, and weights ofprotein and phosphorus contained therein were measured. The protein was650 mg/100 ml and the phosphorus 70.5 mg/100 ml. To remaining 900 ml ofthe supernatant was added calcium chloride to a concentration in thesolution of approximately 1%. pH of the solution was adjusted with 2Nsodium hydroxide to 6.5-7, and white crystals formed were filtered off.Weights of protein and phosphorus contained in the filtrate weremeasured to find that they were 530 mg/100 ml and 8.6 mg/100 ml,respectively. The filtrate, 800 ml in volume was mixed with 95 ml of thepreviously separated casein fraction, and pH of the mixture was adjustedwith sodium hydroxide to around 6.6. To the resulting mixture was addedan emulsifier (Trade name: Exel 300) in a proportion of approximately0.06% to prepare an emulsion.

The emulsion thus produced, 900 ml in volume contained 2.51 g/100 ml ofprotein and 29.5 mg/100 ml of phosphorus (corresponding to 1.17 g ofphosphorus per 100 g of protein), which was favorably used for food asphosphorusreduced cow milk.

If it is intended to adjust weight of the phosphorus to 2.0 g, thecalcium chloride added as above may be to a concentration ofapproximately 0.5%.

INDUSTRIAL APPLICABILITY

The phosphorus-reduced cow milk according to the invention can favorablybe used as food for hyperphosphatemia patients, kidney-disease patientswith impaired calciumabsorbing function and persons of old age.Therefore, the invention is applicable in industrial fields such as foodindustry and pharmaceutical industry.

What is claimed is:
 1. A process for preparing phosphorusreduced cowmilk which comprises adding an acid and/or rennet to cow milk to causeagglutination of casein, separating the agglutinated casein from the cowmilk to obtain a remaining milk serum, adding to the remaining milkserum a calcium salt to precipitate free phosphoric acid contained inthe milk serum as calcium phosphate with lower solubility, removing thecalcium phosphate from the milk serum to obtain a remaining solution,adding to the remaining solution the agglutinated casein to a phosphoruscontent of 1.0-2.0 g per 100 g of protein to obtain a product andemulsifying the product.